Although several studies on the efficacy and the toxicity of exogenous melatonin in Parkinson patients have been carried out, there are no data available on melatonin secretion in these patients. We therefore performed a controlled trial in 9 Parkinson patients (aged 62.1 +/- 8.7 years, x +/- SD) and in 14 control persons (58.0 +/- 10.4 years). Parkinson patients were treated with l-dopa (300-1000 mg per day) in combination with a peripheral decarboxylase inhibitor (benserazide, carbidopa). 14 venous blood samples were taken from each person during a period of 24 hours in order to investigate the circadian secretion pattern of melatonin. Serum melatonin levels were estimated by radioimmuno assay. We found that the circadian secretion patterns of l-dopa-treated Parkinson patients and age-matched controls were very similar except for a phase advance of the nocturnal melatonin elevation in the parkinsonian group.